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 the optimum solution may be to rent the equipment, as necessary. Specialized training is usually
required to operate this test equipment.
System voltages normally operate within a steady-state range of 5 percent plus to 10 percent
minus the nominal system value. This range corresponds to Voltage Range A (referenced in
ANSI C84.1, American National Standard Voltage Ratings for Electric Power Systems and
Equipment (60 Hz)). The voltage range tolerance limits in ANSI C84.1 were established based
on the voltage tolerance limits of ANSI/NEMA MG-1, which establishes the voltage tolerance
limits of the standard induction motor. Since motors are the major component of utilization
equipment load on distribution systems, they were given primary consideration in the
establishment of the voltage standard. Use of the voltage range values in ANSI C84.1 can be
determined for any system voltage because the numbers are established on a 120 V Base. The
proper voltage range for higher voltage systems, therefore, can be taken by multiplying the
transformation ratio of the system times the Base voltage range values. ANSI C84.1 specifies the
voltage at the two important points in the system. The first, is the maximum and minimum at the
point of receipt from the power source. The second, is the minimum at the point of utilization. It
also provides recommended allocations for the voltage drop in the primary distribution system, in
the final distribution transformer, and in the final utilization voltage wiring from the last
transformer to the utilization device. Consideration in developing the recommended ranges
included the effects of high and low voltage on motor and lighting equipment lifetime, output,
and starting characteristics.
8.2.4.1 Voltage Regulation. Voltage regulation, by definition, is the percentage change in
secondary voltage from no-load to full-load conditions. The regulation is customarily specified
at a specific power factor, as the power factor of the load affects the voltage regulation of the
device or circuit. Voltage regulation cannot be improved by the use of the conventional no-load
tap changer on a transformer. The tap changer merely changes the transformer turns ratio, but
does not significantly change the transformer impedance. The regulation (percent change from
no-load to full-load) will, therefore, not change. The operating voltage range will, however,
change and affect the performance of the utilization equipment. As mentioned previously, load
flow studies should be performed and operating conditions (no-load, light-load, or full-load)
examined to ensure that voltage tolerance ranges are not exceeded. If voltage tolerance ranges
are exceeded, then one alternative is to adjust transformer taps to compensate for either high
voltage, at no-load or light-load conditions, or low voltage, at full-load conditions.
Capacitors of either switched or fixed configurations can also be used to correct the voltage range
profile of a distribution system. Often, for large complex systems, the use of switched capacitors
is the only realistic solution for a voltage range that is too wide. In this instance, capacitors are
switched off-line when the load is light, so that the voltage does not become too high. As the
load increases, capacitors are switched on-line to prevent the voltage from becoming too low.
For maximum benefit, capacitors should be located close to the load that is causing the problem,
however, this is often not technically or economically feasible.
8-6
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